Now that I have this fitted, it's working well. It was difficult to fit - the brackets didn't line up with my joists, so I had to fix a piece of wood to the joists, and then fix the brackets to that. This effectively lowered the bottom of the kayak by a couple of inches.
The instructions provided are terrible and do not give sufficient information to fit the hoist. I found useful diagrams on line.
The sling straps don't give many options of different lengths, I shortened them with a sheepshank knot, which isn't ideal.
However, now that it is fitted, it works well and keeps my kayak just out of the way.